\(\displaystyle \int \limits_1^2 \dfrac{1}{x^2}   dx = \)
Rewriting the integrand,
$$ \int \limits_1^2 \dfrac{1}{x^2}   dx = \int \limits_1^2 x^{-2}   dx =$$
$$ = \Big[ -x^{-1} \Big]_1^2 = \left[ -\frac{1}{x} \right]_1^2 $$
$$ = -\left( \frac{1}{2} - \frac{1}{1} \right) $$
$$ = \frac{1}{2} $$